Aircraft towed underwater skip probe



June 27, 1967 c. B. CONVERSE AIRCRAFT TOWED UNDERWATER SKIP PROBEOriginal Filed July 22, 1964 2 Sheets-Sheet 1 INVENTOR new? a 7MATTORNEYS 2 Sheets-Sheet 2 C. B. CONVERSE AIRCRAFT TOWED UNDERWATER SKIPPROBE a]. Filed July 22, 1964 h V Ill/l,

June 27, 1967 Origin ATTORNEYS United. States Patent 3,327,968 AIRQRAFTTOWED UNDERWATER SKIP PRGBE Courtland B. Converse, Marion, Mass,assignor, by niesne assignments, to Francis Associates, Inc., Marion,Mass, a corporation of Massachusetts Continuation of application Ser.No. 384,438, July 22, 1964. This application Apr. 1, 1966, Ser. No.544,653 12 Claims. (Cl. 244-3) This invention relates to the acquisitionof data by underwater sensing devices, and, in particular, to theacquisition of such data by means of an air-towed underwater probe.

This application is a continuation of application Ser. No. 384,438,filed July 22, 1964, and now abandoned.

The determination of various properties of the ocean is important inmany military and commercial applications. Properties such as salinity,temperature, density, and underwater noise affect the propagation ofacoustic energy through water, and therefore affect the performance ofsystems which depend upon the transmission of sonar energy for thetranslation of data. To obtain the required information relative to suchproperties, a great number of measurements must be taken over arelatively large area, and therefore the measurement rate is animportant consideration. Similarly, when searching for the presence ofsubmarines by means of sonar devices, it is desirable to sample thelargest area of water in the shortest possible period of time.

In all of the above cases, the utility of prior art oceanographicdevices has been limited by the speed at which the various measurementscan be taken. The maximum speed of a boat is an obvious limitation, and,moreover, when operating from a rapidly moving surface vessel, theacoustic noise generated by the vessel deleteriously affects theoperation of sonar devices. To overcome this drawback, it has beenproposed to incorporate sonar devices in probes which are dunked fromhelicopters. The hovering helicopter provides a quite environment foroperation of the sonar equipment, while its relatively high cruisingspeed may be used to sample large areas of the water. However, even ahelicopter system is limited as to the rate at which measurements can bemade and the relatively short range of a helicopter.

Accordingly, it is an object of the present invention to provide amethod and apparatus for obtaining underwater data more rapidly thanheretofore possible.

A more specific object of the invention is to provide a method andapparatus for obtaining underwater data from an air towed probe.

Another object of the invention is to provide a method and apparatus forobtaining underwater data in which the low noise advantage of ahelicopter system is maintained, while the sampling rate is materiallyincreased.

Still another object is to provide an improved probe for use inobtaining underwater data at high speeds.

Briefly, the invention includes a probe, designed to obtain the desireddata, towed on an elastic cable by an airplane. When the cable is slack,the probe falls slowly through the water, during which time the desireddata is obtained. As the airplane continues to move in a straight line,the cable becomes tensioned and stretches, thus storing potentialenergy. The tensioned cable exerts a force on the probe whichaccelerates it up through the water. Once free from the water, thepotential energy on the cable is imparted to the probe so that itaccelerates to a high degree and flies out of the water to a newlocation, at which the cable again is slack. The cycle continues torepeat in a stable manner.

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The manner in which the above and other objects of the invention areaccomplished is more fully described below with reference to theattached drawings wherein:

FIG. 1 is a schematic diagram of the probe cable and airplane indicatingthe manner in which the invention opcrates;

FIG. 2 is a perspective view of a preferred embodiment of the probe;

FIG. 3 is a front view of the probe illustrated in FIG. 2;

FIG. 4 is a sectional view along the line 44 of FIGS. 2 and 3;

FIG. 5 is a top view of the rear portion of the probe;

FIG. 4 is a perspective view of one type of elastic cable useful withthe invention; and

FIG. 7 is a perspective view of a second embodiment of an elastic cable.

In the following specification and claims, the invention is not to beconstrued as limited to the acquisition of any specific type of data.The invention would have particular utility in an anti-submarine systemin which sonar pings are emitted, and their reflections heard during thefree fall period of the probes descent. However, the invention wouldhave equal utility in measuring properties of the water such astemperature, salinity, etc., by means of conventional sensing devicessuch as thermistors or the like. In the following specification, neitherthe location of the data receiving circuitry nor the placement of therequired transducers has been illustrated in the drawings, since theseare matters of mere technical expedience to those skilled in the art.

FIG. 1 is a schematic diagram of the invention showing its mode ofoperation during a normal cycle. In accordance with the invention, aprobe It) is connected to an aircraft 12 by means of an elastic cable14. Elastic cable 14 may comprise conventional cable portions 14a and14b, between which is sandwiched a highly resilient section 140. A bodyof water is illustrated at 16 and the flight path of aircraft 12 shownas a solid line 18 through the longitudinal axis of the plane.

In FIG. 1 four different positions of the aircraft cable and probe areshown. The cycle is considered to start at time T0 at which point theaircraft is at the extreme left of FIG. 1, probe 10 at the surface ofwater 16, and cable 14 in a slack condition between aircraft 12 andprobe 10, with resilient portion in its normal or non-stretchedcondition.

During the first portion of this cycle, probe 10 descends verticallyalong the path indicated by dotted line 21. The vertical descent of theprobe comprises the data acquisition portion of the cycle and occurs asthe probe effectively free falls through the water. During this periodthe desired data is obtained and returned to the aircraft via the cable,or it may instead be recorded by suitable means in the probe itself.

While the probe is descending, aircraft 12 continues along its path 18to a position indicated at time T1. At time T1, resilient cable portion140 has been extended to its maximum length. At this time, the potentialenergy stored in the tensioned portion 140 starts to accelerate theprobe to a velocity considerably above that of the aircraft 12, and theprobe moves along path 21 to the surface of the water, which it reachesat time T2. Due to the great differential in the density of sea waterand air, the acceleration of the probe as it leaves the water at time T2will cause the probe to fly ahead of aircraft 12 in a ballistictrajectory 21" and again land in the water at time T3 to repeat the freefall and data acquisition period. The next cycle continues from time T3in the identical manner.

The actual collection of the desired data forms no part of the presentinvention and therefore is not described herein. If required, pressuretransducers or similar triggering mechanisms can be used to activate thesonar equipment or sensing devices within the probe at specified depths.

The invention above described is not limited to a particular type ofcable, nor is it limited to a particular probe; however, FIGS. 25illustrate a novel probe of particular utility in the inventionillustrated in FIG. 1. As explained in detail hereinbelow, the probeincludes special provisions to prevent its free-falling descent throughthe water from generating noise which would interfere with datacollected by sonar equipment.

The probe comprises a torpedo shaped fuselage including conically shapedfront and rear sections a and 100, respectively, joined by a cylindricalcentral section 1%. The rear section 10c of the fuselage includes fourstabilizing fins 22 positioned in quadrature to help stabilize the probeduring its free falling descent. At the forward portion of centralfuselage section 10b a pair of downwardly canted triangular fins 24similarly guide the probe during its ascent. The manner in which fins 22and 24 exert a stabilizing influence on the probe is conventional.

If, during the measuring portion of the cycle, the probe descendsvertically into the Water at too high a rate of speed, the noise signalsgenerated may interfere with the operation of sonar equipment within theprobe. Accordingly, in a preferred embodiment, the probe includes aunique braking mechanism to retard the probes descent during the dataacquisition period of the cycle, without reducing the speed of the probeduring its upward travel through the water under the influence of theelongated elastic cable section 140. The braking mechanism might alsoserve to control the probes rate of descent in the event it is desiredto record the property sensed by the probe as a function of depth.

According to the invention, the braking mechanism comprises twooppositely disposed rectangular plates 26 shaped to fit flush withincomplementary windows of the rear fuselage section 100. Plates 26include inwardly extending flanges 28, and are pivotally secured to thefuselage by means of pins 30 passing through suitable apertures in theforward portions of flange 28 and cooperating portions of fuselagesection 100.

The brake plates 26 include elongated members 32 extending inwardly fromthe forward end of flange 28. At the inner extremity of each member 32there is a follower 34 which is actuated by one of plates 36 or 38 toapply or remove the braking force.

Plates 36 and 38 are secured to a longitudinal rod 40 which extendsaxially through the probe 10 and termimates in a blunt nose piece 42 atthe forward extremity of the probe. Nose piece 42 is blunted tostabilize the probe at impact and for a short time thereafter bypreventing re-exit characteristics and skipping. Rod 40 is slidablymounted in five central discs 44, 45, 46, 47 and 48 of the probe 10. Agenerally rectangular plate 50 is slidable in a slot 52 within centralprobe section 1012. Cable portion 14b is coupled through the crosspieceof a U-shaped bracket 54 pivotally secured to plate 50 by means of pin56. Plate 50 is immovably fixed to the rod 40 by means of screws 58 orthe like. A clip 60 secures the cable portion 14b to the plate 50, andthe cable is introduced into the central portion of the probe so thatthe cable may be used to transmit the received data back to the plane.

During operation, and prior to the descent of probe 10 along path 21,the nose piece 42 is forward in the position illustrated in dashed linesin FIG. 4. In this position, plate 50 is pulled to the forward portionof slot 52, and plate 38 pushes followers 34 forward so that the brakeplates 26 are closed, i.e. fiush with the fuselage surface. When theprobe descends into the water, the impact of the nose piece 42 and thewater pushes the nose piece and rod 40 backwardly to the illustratedsolid line position, When this occurs, plate 36 pushes followers 34backward, pivoting the brake plates 26 open. The open plates abruptlybrake the descent and the probe falls during the data acquisitionportion of the cycle at a substantially reduced rate of speed toappreciably limit the noise signals generated.

When plane 12 reaches the position indicated at time T1 in FIG. 1, andthe elongated elastic cable portion 14c begins to pull the probe 10toward the surface, the cable pulls plate 50 and rod 40 forward withrespect to the probe body so that nose piece 42 returns to the dottedline position. In this position, plate 38 pushes followers 34 forwardcausing the brake plates 26 to pivot back into the body of the probe.Hence, during the upward movement of the probe through the water, thebrake plates exert no impeding force upon the probes movement. Thebrakes remain closed until the nose piece 42 again strikes the surfaceof the water at time T3 and the cycle repeats.

There are various types of cable which may be used as the elasticportion 14c. Cable portions 14a and 14b may be conventionalnon-stretchable cable, and there are commercially available elasticcables which will suffice for the cable portion 140. Two preferredembodiments of the elastic cable portion are illustrated in FIGS. 6 and7.

In FIG. 6, the cable includes an elastic core 70, made of rubber or thelike, with wires 72 and 74 helically wound in opposite directions overits outer surface. Wires 72 and 74, together with central core 70, areenclosed in an annular elastic casing 76 which also may be made ofrubber. When the cable illustrated in FIG. 6 is tensioned, the helicalwires 72 and 74 stretch to a relatively straight configuration toaccommodate the elasticity of the core 70 and casing 76.

The cable illustrated in FIG. 7 is similar to that of FIG. 6. In thisembodiment, the cable comprises a plurality of tightly packed elasticbands 78 covered by an elastic fabric 80. Three wires 82, 84 and 86 arecoiled around the tube thus formed and enclosed in a second elasticfabric 88. When the cable is stretched, the wires elongate in the mannerof a tensioned coil spring.

The aircraft 12, in addition to including the electronic equipmentnecessary to trigger and receive data from the probe, must include awinch or the like to deploy and retrieve the cable and probe. It isnecessary that when the probe reaches the water there be suflicientcable left to permit the cycle described above to commence. At highspeeds, at winch drum could be used to deploy the wire axially from theend of the drum. If the cable and probe can be deployed slowly, atstandard target winch, such as those used in naval aircraft gunnarysystems, could be employed.

By way of example only, the entire cable may be approximately 5000 feetlong, 164 feet of which is the elastic portion 140 with a springconstant of 6.85 pounds per foot. The probe selected may have the samedrag properties as a sphere 6 inches in diameter. The plane may betravelling at a speed of about 100 knots at an altitude of 656 feet.Under these conditions, the probe will sink to a depth of about feet inapproximately 11 seconds with the cycles repeating every 2500 feet.

Although a preferred embodiment of the invention has been shown anddescribed, the invention is not so limited and should only be defined bythe following claims.

What I claim is:

1. A method of obtaining data within a body of water from a movingaircraft, comprising the steps of towing a probe from the aircraft on acable having elastic properties, permitting said probe to periodicallyfall through the body of water while obtaining such data and causingsaid cable to be stretched elastically by a substantial amount toaccelerate the probe out of the body of the water and to cause the sameto leap through the air to another location in the body of water.

2. A method according to claim 1, including the step of braking theprobe when it is falling through the water.

3. A method according to claim 2, including the step of removing thebraking force when the probe is rising through the water under theinfluence of the tensioned cable.

4. A method of obtaining data from within a body of Water by a probetowed by a moving aircraft, comprising the steps of towing the probefrom the aircraft by means of a cable having elastic properties,permitting said probe to fall through the water while obtaining suchdata and simultaneously stretching the cable a substantial amount toaccelerate the probe out of the water and to another location at whichpoint the cable is slack, and again permitting the probe to fall throughthe water until the cable is stretched said substantial amount.

5. A method according to claim 1, including the steps of braking theprobe when it is falling through the water, and removing the brakingforce when the probe is rising through the water under the influence ofthe tensioned cable.

6. Apparatus for acquiring data by a moving aircraft from a body ofwater, comprising a sensor and means being elastic to a substantialdegree and adapted to be secured to the aircraft for towing the sensorfor periodically immersing said sensor in the body of water and foraccelerating said sensor through the air to a new immersion location ata speed greater than the speed of said aircraft.

7. Apparatus for acquiring data from an aircraft towed probe within abody of water, comprising a probe and an elongated cable secureddirectly to one end portion of said probe, the other end portion of saidcable being adapted to be secured to said aircraft, at least a portionof said cable being elastic to a substantial degree so that stretchingof the cable during movement of the aircraft is sufiicient to acceleratethe probe out of the water and to another location.

8. Apparatus according to claim 6, wherein said probe includes means forbraking the fall of the probe through the water.

9. Apparatus according to claim 8, including means for removing thebraking force when the probe is accelerated upwardly through the water.

10. Apparatus according to claim 7, wherein said elastic portion of thecable includes an elastic core and at least one wire wound on said corefor transmitting a signal.

11. A probe for obtaining aquatic data, comprising an elongated bodyportion, at least two brake plates pivotally secured to said bodyportion and normally flush therewith, a forward nose piece axiallyslidable with respect to said body portion, and a connecting memberbetween said nose piece and said brake plates whereby movement of saidnose piece toward said body portion pivots said brake plates away fromsaid body portion.

12. A probe according to claim 11, wherein said connecting memberincludes actuating means and said brake plates include means extendinginto the path of movement of said actuating means.

References Cited UNITED STATES PATENTS 2,590,131 3/1952 Schonstedt 244-33,159,806 12/1964 Piasecki 114235 X MILTON BUCHLER, Primary Examiner.

T. MAJOR, Assistant Examiner.

1. A METHOD OF OBTAINING DATA WITHIN A BODY OF WATER FROM A MOVINGAIRCRAFT, COMPRISING THE STEPS OF TOWING A PROBE FROM THE AIRCRAFT ON ACABLE HAVING ELASTIC PROPERTIES, PERMITTING SAID PROBE TO PERIODICALLYFALL THROUGH THE BODY OF WATER WHILE OBTAINING SUCH DATA AND CAUSINGSAID CABLE TO BE STRETCHED ELASTICALLY BY A SUBSTANTIAL AMOUNT TOACCELERATE THE PROBE OUT OF THE BODY OF THE WATER AND TO CAUSE THE SAMETO LEAP THROUGH THE AIR TO ANOTHER LOCATION IN THE BODY OF WATER.